THE ANODIC BEHAVIOR OF IRON IN ANHYDROUS DIMETHOXYETHANE AND PASSIVATION BY SOLVENT ELECTROPOLYMERIZATION

The corrosion and passivity of high purity iron in anhydrous dimethoxyethane with 0.5M LiAsF6 have been studied by various electrochemical and surface analytical techniques. The motivations for this study were twofold; (i) to develop an understanding of the passivity of metals and alloys in anhydrous organic solutions at a fundamental level, and (ii) to apply what is learned to improve the performance and useful life of high energy density lithium batteries which employ organic solvents. The data show that iron displays a stable passive region with low current densities over a large range of anodic potentials. Several different passivation mechanisms have been identified in this stable region. Among these mechanisms is passivation by solvent chemisorption. Our key finding is the observation of passivation by electropolymerization of the dimethoxyethane solvent. The polymerization reaction has not been observed when electrolytes other than LiAsF6 are used. Consequently, the potential at which breakdown of passivity occurs is lower in solutions containing alternative electrolytes. In addition, a bare oxide-free metal surface appears necessary for initiation of the electropolymerization reaction.